<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width,initial-scale=1.0">
  <title>弹性框 - 响应式布局</title>
  <style>
    body {
      margin: 0;
    }
    .container {
      display: flex;
    }
    .box {
      width: 100px;
      height: 30vh;
    }
    .b1 {
      background: #009;
    }
    .b2 {
      background: #06c;
    }
    .b3 {
      background: #39f;
    }
    .b4 {
      background: #6cf;
      width: 50px;
    }
  </style>
</head>
<body>
  <div class="container">
    <div class="box b1"></div>
    <div class="box b2"></div>
    <div class="box b3"></div>
    <div class="box b4"></div>
  </div>
</body>
</html>
